Pagination with Lightning Components

Question

I am trying to implement a simple paginator that uses a wrapper object to move between pages, but I am not sure how to get the wrapper class to work in the component controller. Specifically my questions are:

1. How to invoke the inner-class method void next() from the component controller, given it is not a getter?
2. Can I call non-Aura methods from the component controller?
3. Can I call non-static methods from the component controller?

The documentation clearly answers questions 2 & 3 with a "no," but I wanted to be sure just in case there were exceptions to the rule.

The following code is not compiling with this error:

AuraEnabled methods must be named with a prefix 'get'

public class PageController
{
    @AuraEnabled
    public static QueryCursor getAccounts()
    {
        return new QueryCursor();
    }

    public class QueryCursor
    {
        private Integer m_pageNumber;

        public QueryCursor()
        { 
            m_pageNumber = 1; 
        }

        @AuraEnabled
        public Account[] accounts
        { 
            get { return queryAccounts(m_pageNumber); } 
            private set; 
        }

        @AuraEnabled
        public void next() 
        { 
            m_pageNumber++; 
        }

        private Account[] queryAccounts(pageNumber)
        {
            // return Accounts with an offset
        }
    }
}

I understand why I'm getting the error, but I don't want to change the signature from void next() to Account[] getNext(). What's the best way to go about this?

Answer 1

Pagination isn't accomplished server-side in Lightning; but instead done by client-side code. See my gist for an example that loads up to 50,000 rows. If you need more than that, you simply need to load the data from the server in pieces, as demonstrated here; basically, just query X number of records, and if there's still more data to get, use the ID as a condition for the next query to get the next "page" of data. Lightning is fast enough that you should be sorting and paging client-side without resorting going back to the server all the time.

Answer 2

The Dreamhouse App has some code for server-side Pagination. The initial page load is faster than loading 1000+ records, but the first time you load the next / previous page it is slower. With action.setStorable(), subsequent visits to the pages are much faster. Like anything, there are trade-offs. For the full implementation, install the Dreamhouse app in a Developer org.

Here's my modified version of the Apex Class and an @AuraEnabled method that gets records using the PagedResult class.

public with sharing class PagedResult {
    @AuraEnabled
    public Integer pageSize { get; set; }

    @AuraEnabled
    public Integer page { get; set; }

    @AuraEnabled
    public Integer total { get; set; }

    @AuraEnabled
    public List<Object> results { get; set; }
}

then in your Apex Controller for your Lightning component you'd have

@AuraEnabled
public static PagedResult getPagedRecords(String sObjectName, String fieldNames, Decimal pageSize, Decimal pageNumber) {
    Integer pSize = (Integer)pageSize;
    Integer offset = ((Integer)pageNumber - 1) * pSize;
    PagedResult pr =  new PagedResult();
    String totalQuery = 'SELECT Id FROM ' + sObjectName;
    pr.pageSize = pSize;
    pr.page = (Integer) pageNumber;
    String query = 'SELECT ' + fieldNames + ' FROM ' + sObjectName;
    pr.total = Database.query(totalQuery).size();
    pr.results = Database.query(query + ' LIMIT :pSize OFFSET :offset');
    return pr;
}

Answer 3

I would say consider looking at the standard set controller, it has build in methods for pagination so you could have aura exposed methods that call the corresponding method on the standard set controller. And probably have the std set controller as a private property